US20060073394A1 - Reduced mask count gate conductor definition - Google Patents
Reduced mask count gate conductor definition Download PDFInfo
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- US20060073394A1 US20060073394A1 US10/711,758 US71175804A US2006073394A1 US 20060073394 A1 US20060073394 A1 US 20060073394A1 US 71175804 A US71175804 A US 71175804A US 2006073394 A1 US2006073394 A1 US 2006073394A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
- H01L21/3205—Deposition of non-insulating-, e.g. conductive- or resistive-, layers on insulating layers; After-treatment of these layers
- H01L21/321—After treatment
- H01L21/3213—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer
- H01L21/32139—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer using masks
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/027—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34
- H01L21/033—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising inorganic layers
- H01L21/0334—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising inorganic layers characterised by their size, orientation, disposition, behaviour, shape, in horizontal or vertical plane
- H01L21/0337—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising inorganic layers characterised by their size, orientation, disposition, behaviour, shape, in horizontal or vertical plane characterised by the process involved to create the mask, e.g. lift-off masks, sidewalls, or to modify the mask, e.g. pre-treatment, post-treatment
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/027—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34
- H01L21/033—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising inorganic layers
- H01L21/0334—Making masks on semiconductor bodies for further photolithographic processing not provided for in group H01L21/18 or H01L21/34 comprising inorganic layers characterised by their size, orientation, disposition, behaviour, shape, in horizontal or vertical plane
- H01L21/0338—Process specially adapted to improve the resolution of the mask
Definitions
- the invention relates to semiconductor fabrication, and more particularly to fabricating a combination of small and large structures.
- SIT sidewall image transfer
- SIT is able to produce structures substantially narrower than the minimum size achievable with photolithographic techniques, while maintaining excellent width control.
- SIT methods produce structures, usually hard masks, of generally closed-loop geometry. These loops have a single, well-controlled width (referred to henceforth as the “critical image width”).
- Conventional SIT applications thus require the use of two additional masks. One, called a “loop cutter mask”, is employed to segment the loops, and a second, called a wide-area mask, is employed to add shapes of any other, usually wider, dimensions.
- a method of combining the wide-image mask and loop-cutter mask includes protecting a critical portion of a loop-geometry hard mask on a substrate with a first portion of a follow-on mask, and forming a wide-area pattern on the substrate proximate the hard mask with a second portion of the follow-on mask. The method also includes removing an exposed portion of the hard mask, and subsequently exposing the critical portion of the hard mask.
- a method of combining a wide-image mask and a loop-cutter mask includes forming a follow-on mask in a loop-cutter pattern on a portion of a hard mask, wherein the follow-on mask comprises a wide-image section and narrow-image section, and removing a portion of the hard mask left exposed by the follow-on mask.
- the method also includes removing at least a portion of the narrow-image section of the follow-on mask.
- the method also includes employing remaining wide-image sections of the follow-on mask to pattern wide-area shapes under the hard mask and follow-on mask.
- a combined wide-image and loop cutter mask in another aspect of the invention, includes a follow-on mask formed over a hard mask, and a wide-image section forming a first portion of the follow-on mask.
- a narrow-image section forms a second portion of the follow-on mask.
- the follow-on mask is configured to have the narrow-image section preferentially removed while the wide-image section remains substantially able to mask underlying films.
- FIG. 1 is an illustration of a SIT hard mask before trimming
- FIGS. 2-5 illustrates steps in an embodiment of forming a wide-image and loop-cutter pattern in accordance with the invention
- FIGS. 6-8 illustrates steps in an embodiment of forming a wide-image and loop-cutter pattern in accordance with the invention
- FIGS. 9-13 illustrates steps in an embodiment of forming a wide-image and loop-cutter pattern in accordance with the invention.
- FIGS. 14-16 illustrates steps in an embodiment of forming a wide-image and loop-cutter pattern in accordance with the invention.
- the invention relates to semiconductor fabrication, and more particularly to fabricating a combination of small and large structures.
- a reduction in the number of masks required to form a final image especially when combining SIT imaging processes with traditional masking techniques is possible.
- the method of the invention generally includes, for example, forming a follow-on mask over a section of a sidewall image transfer (SIT) loop on a substrate for further imaging the underlying substrate.
- SIT sidewall image transfer
- a hard mask 10 image in the form of a SIT loop built using SIT-related techniques is shown.
- a hard mask loop 10 any imaging technique which builds a continuous, single-width loop, especially a single-width loop of very small and precise width, is suitable for use with embodiments of the invention.
- the SIT loop or hard mask 10 is on the order of a few tens of nanometers wide.
- embodiments of the invention are suitable for use with loops, or any hard mask image of virtually any size suitable for use in a semiconductor device.
- dashed lines indicating the target shape 12 of the final image.
- the target shape 12 is the final shape to which the underlying substrate will be formed using the hard mask loop 10 and a follow-on mask.
- the target shape 12 includes a wide section 14 and a narrow section 16 .
- the wide section 14 of the target shape 12 overlaps the hard mask loop 10 ; whereas, the narrow section 16 of the target shape 12 coincides with a portion of the hard mask loop 10 .
- the follow-on mask should protect 1) desired portions of the SIT-defined critical-dimension masking loop; and 2) less-critical, usually wider regions to be used, for example, for long-channel devices or contact pads. Portions of loop to be removed should be left uncovered. After etch/removal of unwanted loop material, removal of the part of the follow-on mask covering critical-dimension SIT-defined lines is desirable.
- a follow-on mask 18 is formed over a portion of the hard mask loop 10 .
- the follow-on mask 18 includes a wide section 20 , which corresponds to the wide section 14 of the target shape 12 .
- the follow-on mask 18 also includes a narrow section 22 which corresponds to the narrow section 16 of the target shape 12 .
- the follow-on mask 18 may be formed by any of the methods well know in the art suitable for forming a follow-on mask over a hard mask loop including, expanding a desired wide-feature design by an undercut/ashback amount, and adding tabs to cover desired portions of the hard mask loop 10 .
- the process includes printing a single follow-on mask 18 .
- the patterns for mask 18 are created by expanding desired wide-poly designs by an undercut/ashback amount, and adding tabs to cover desired SIT-defined width regions. This produces a single gate-conductor follow-on mask which is a combined wide-image and loop-cutter pattern.
- the unwanted, uncovered regions of the hard mask loop loop 10 are etched away from the substrate 5 .
- the unwanted sections of the hard mask 10 may be removed using any of the suitable etching techniques well known in the art for removing the hard mask material. In other words, unwanted SIT-defined hard mask loop portions are removed/etched, without stripping resist.
- the follow-on mask 18 (see FIG. 3 ) is etched in such a way as to reduce its length and width along its edges. Accordingly, in some instances, the narrow section 22 of the follow-on mask 18 will be almost completely etched away. The narrow section 22 of the follow-on mask 18 is at least etched away sufficiently to expose the underlying critical edges of the hard mask loop 10 . In other words, the process includes pulling back the follow-on mask 18 so that the narrow section 22 covering desired portions of the hard mask loop 10 are removed (at least the critical edges of the SIT line are uncovered).
- the narrow section 22 of the follow-on mask 18 has been completely removed to expose the underlying remaining hard mask loop 10 section. Additionally, the wide section 20 of the follow-on mask 18 has its length and width reduced to produce an image pad 24 . The image pad 24 substantially conforms to the wide area 14 of the target shape 12 . Additionally, the remaining exposed portion of the hard mask loop 10 , formerly covered by the narrow section 22 of the follow-on mask 18 corresponds to the narrow section 16 of the target shape 12 .
- the etching of the follow-on mask 18 to form the image pad 24 may be performed by any of the methods well known in the art suitable for etching a follow-on mask on top of a hard mask loop 10 section and substrate 5 .
- the structure is used as a mask for etching the underlying substrate 5 . Accordingly, once the underlying substrate 5 has been etched, a structure of the underlying substrate 5 in the shape of the target shape 12 is formed where a portion of the final structure is shaped using the critical edges of the hard mask. In one embodiment, this includes etching the gate conductor stack using a combination of SIT-loop for the device-Lpoly section, plus resist pad for the wide section, and then stripping masking layers.
- the final shape of the underlying substrate 5 may additionally include a stub 26 in addition to the target shape 12 .
- the stub 26 is a consequence of the pull-back process of the wide area 20 of the follow-on mask 18 exposing additional portions of hard mask loop 10 . In most applications, this stub 26 is an inconsequential artifact which has no effect on fabrication process or the circuit design. In other applications, the stub 26 may be a beneficial component to the final shape 28 .
- the target image shape 12 is shown having a wide section 14 and a narrow section 16 .
- the narrow section 16 of the target shape 12 corresponds to the critical edges of the underlying hard mask loop 10 .
- the follow-on mask 18 includes a wide section 20 and a narrow section 22 .
- one purpose of the narrow section 22 of the follow-on mask 18 is to preserve the underlying section of hard mask 10 during the hard mask loop 10 cutting or etching process.
- the narrow section 22 of the follow-on mask 18 should extend beyond the edges of the hard mask loop 10 in order to protect those precision or critical edges.
- the amount by which the follow-on mask 18 extends beyond the edges of the underlying hard mask loop 10 is the overlap 32 .
- the amount by which the follow-on masks 18 extends beyond the edges of the wide section 14 of target image 12 is the extended section 30 .
- the extended section 30 is generally larger than the overlap 32 .
- the amount by which the target image 12 is extended to form the follow-on mask 18 should preferably be sufficient so that despite follow-on mask 18 registration and image size errors, substantially all critical edges of the underlying hard mask 10 material remain covered during the loop etching process to avoid degrading the wanted portions such as the precision edges of the hard mask 10 .
- FIG. 7 an illustration of the effects of a mis-registered follow-on mask 18 is shown.
- the follow-on mask 44 has been formed in mis-alignment and pull-back etched.
- the amount of pull-back 34 need not remove the entire width of narrow section 22 as long as critical edges of hard-mask loop section 10 are exposed despite some amount of mis-alignment.
- the minimum image pad space 36 density is related to the minimum lithographic pad-pad space 38 of two follow-on masks, 18 and 1 9 , achievable with the method of the invention.
- the minimum image pad space 36 is related to the extended section 30 ( FIG. 7 ).
- pad shapes on follow-on mask 18 should be sufficiently far apart to allow a minimum space to print between expanded adjacent pads.
- FIGS. 9-13 another embodiment of a combined wide-image and loop-cutter pattern is shown.
- a hard mask loop 10 is formed on a substrate 5 .
- An outline of the target shape 12 is shown by a dashed line.
- the target shape 12 has a wide section 14 and a narrow section 16 .
- the follow-on mask 46 has a narrow section 48 and a wide section 50 , corresponding to the wide and narrow sections 14 , 16 , respectively, of the target shape 12 .
- the dimensions of the wide section 50 of the follow-on mask 46 approximately correspond to the dimensions of the wide section 14 of the target shape 12 . Accordingly, the narrow section 48 of the follow-on mask 46 extends or overlaps beyond the edges of the underlying hard mask loop 10 . The edges of the wide section 50 of the follow-on mask 46 also extend beyond the edges of the underlying hard mask loop 10 while still corresponding to the dimensions of the wide section 14 of the target shape 12 . Additionally, an edge of the wide section 50 may be configured to coincide with edge of the hard mask loop 10 . Thus, the wide section 50 of the follow-on mask 46 does not contain a section expanded beyond the underlying image shape 12 . In other words, this embodiment is similar to the previously discussed embodiment, except that while critical-width line portions of designs are expanded to make the narrow sections 48 of follow-on mask 46 , the follow-on mask pads 50 are not expanded.
- the undesired exposed portions of the hard mask loop 10 are etched from the surface of the substrate 5 .
- the follow-on mask 46 protects any hard mask loop 10 underlying the follow-on mask 46 .
- the original hard mask loop 10 is formed into hard mask loop 10 sections, where each section corresponds to a follow-on mask 46 .
- the follow-on mask 46 has been pulled back to form a core pad 52 .
- the narrow section 48 of the follow-on mask 46 has been etched away to expose the underlying hard loop mask 10 , thus exposing the edges of the hard mask loop 10 .
- the follow-on mask 46 may be pulled back by any of the methods well known in the art suitable for etching the material forming the follow-on mask 46 , but which does not etch the hard mask loop 10 material.
- a simple oxygen-based etch (ash) maybe used if the thickness of the follow-on mask 46 is sufficient.
- the core pad 52 is then re-grown along its edges to expand its length and width to form an image pad 54 .
- the image pad 54 is formed either over a section of hard mask loop 10 on top of the substrate 5 or over a core pad 52 employed for patterning shapes not attached directly to portions of the hard mask loop 10 .
- the core pad 52 is then grown back to approximately its original size using a side wall deposition and directional-etch process. The directional-etch portion of this process should have sufficient over etch to remove deposited material from the sidewalls of hard mask loop 10 , which thus must be thinner than the sidewall height of core pads 52 .
- the combination (shown as reference numeral 56 ) of the image pad 54 and the remaining section of the hard loop mask 10 is used as a mask to etch the final shape into the underlying substrate 5 .
- the image pad and section of hard mask loop 10 are removed. It should be noted that this method of combined wide-image and loop-cutter does not produce the stub 26 shown in FIG. 5 . Additionally, the minimum pad-pad distance is decreased because the wide section 50 of the follow-on mask 46 does not need to extend beyond the edges of the target shape 12 .
- the above method allows multiple initial follow-on masks 46 to be placed close to one another.
- image pads cannot be made with dimensions less than twice the pull-back distance, and thus either the minimum image pad size is limited or the pull-back distance is limited, both of which place size limitations on the target shape.
- minimum pad-to-pad distance is decreased, but this method may be less effective for making pads with dimensions less than twice the pull-back/regrow distance plus enough to keep the desired structures in place.
- FIGS. 14-16 another embodiment of a wide-image and loop-cutter combination pattern is shown.
- a substrate 5 has a hard mask loop 10 formed on its surface.
- a follow-on mask 58 is Formed over the hard mask loop 10 .
- the follow-on mask 58 includes a narrow region 62 and a wide region 60 .
- a target shape 12 is indicated by the dashed lines.
- the target shape 12 has a wide area 14 and a narrow section 16 .
- the narrow section 62 of the follow-on mask 58 is formed at a reduced thickness as compared to the wide section 60 of the follow-on mask 58 .
- the narrow section 62 of the follow-on mask 58 is typically about 25% thinner than the wide section 60 of the follow-on mask 58 although other differences in thickness are also contemplated.
- the narrow section 62 of the follow-on mask 58 may be formed at a reduced thickness by any of the methods well known in the art for forming a thinner mask.
- the reduced thickness of mask 58 in narrow section 62 is formed by operating the imaging tool so that narrow section 62 is of a dimension approaching the resolution limits of the tool.
- the follow-on mask 58 will generally rely on degradation of resist profiles when smaller lines are printed. Additionally, it is well known to those of skill in the art that using photolithography to print “properly out of focus” narrow lines can maintain good nominal line width control, but degrade in as-developed resist height. Thus, the thinned narrow section 62 of the follow-on mask 58 may be printed concurrently with the wide section 60 of the follow-on mask 58 . Additionally, the narrow section 62 of the follow-on mask 58 overlaps, i.e., extends beyond the critical edges of the hard mask loop 10 .
- the unwanted exposed portion of the hard mask loop 10 is etched or otherwise removed.
- the unwanted portions of the hard mask loop 10 are removed while the critical portions of the hard mask loop 10 are protected and remain intact under the follow-on mask 58 .
- this embodiment uses a mask created from line and pad data very similar to that used for previously discussed embodiments.
- critical SIT-defined regions have design expanded by an overlap amount so that critical edges of the hard mask loop 10 are protected despite overlay and image size variability.
- the follow-on mask 58 is vertically etched.
- the thin narrow section 62 (of FIG. 14 ) of the follow-on hard mask 58 is preferentially removed, while the thick wide section 60 (of FIG. 14 ) of the follow-on mask, while also being etched, will remain upon the completion of the vertical etch.
- the remaining structure includes an image pad 64 which corresponds to the original wide section 60 of the follow-on mask and an exposed section of the hard mask loop 10 .
- the image pad 64 and the remaining section of the hard mask 10 form a mask corresponding to the target shape 12 . Additionally, the critical edges of the section of the hard mask 10 are now exposed after having been protected during the hard mask etch step. In other words, vertically strip the follow-on mask 18 pattern so that the thinned areas are completely removed, but areas with full-height resist remain.
- the substrate 5 is etched using the combination of the image pad 64 and remaining section of the hard mask 10 as a mask to form the final shape 66 in the substrate 5 .
- the final shape 66 corresponds to the target shape 12 and is formed by a combination of portions of the original follow-on mask 58 (shown in FIG. 14 ) and exposed portions of the hard mask 10 .
- the minimum pad-to-pad distance is decreased over previously discussed embodiments. Also, it is possible to design pads with small dimensions as long as they are large enough so that they do not suffer resist thinning during follow-on mask 18 printing.
- methods include depositing on a section of the SIT loop an oversized follow-on mask of the final image, and etching the mask uniformly to leave a final large area image while removing those portions of the follow-on mask covering critical edges of the SIT loop.
- those portions of the SIT loop having critical edges which will contribute to the final image are covered during the SIT loop cutting process. After SIT cutting, the edges are re-exposed for the final etch in order to take advantage of the high tolerances possible with SIT image forming methods.
Abstract
Description
- The invention relates to semiconductor fabrication, and more particularly to fabricating a combination of small and large structures.
- As the size of semiconductor devices has decreased, photolithographic techniques become unable to reliably create structures of the dimensions required. As photolithographic techniques have become unusable, other technologies have been developed to create the small structures required by the ever shrinking semiconductor devices. One example of a non-photolithographic imaging technique is sidewall image transfer (“SIT”).
- SIT is able to produce structures substantially narrower than the minimum size achievable with photolithographic techniques, while maintaining excellent width control. However, SIT methods produce structures, usually hard masks, of generally closed-loop geometry. These loops have a single, well-controlled width (referred to henceforth as the “critical image width”). Conventional SIT applications thus require the use of two additional masks. One, called a “loop cutter mask”, is employed to segment the loops, and a second, called a wide-area mask, is employed to add shapes of any other, usually wider, dimensions.
- Accordingly, subsequent processing is required to remove the unwanted portions of the closed-loop structures produced by SIT. While removing unwanted loop material with the loop-cutter mask, both edges of loop material which define portions of critical width images must be protected in order to maintain the excellent image size control afforded by SIT techniques. Both of these edges must subsequently be left exposed during etch of underlying films in order to accurately transfer their pattern into those underlying films.
- Furthermore, not all structures being formed are to be of the same small dimensions typically produced by SIT methods. Wider shapes are often required, for example, to fabricate contact landing pads.
- Combining other imaging processes with SIT methods to produce structures of varying dimensions, with some of those dimensions smaller than those achievable by photolithographic techniques, is typically required.
- In a first aspect of the invention, a method of combining the wide-image mask and loop-cutter mask includes protecting a critical portion of a loop-geometry hard mask on a substrate with a first portion of a follow-on mask, and forming a wide-area pattern on the substrate proximate the hard mask with a second portion of the follow-on mask. The method also includes removing an exposed portion of the hard mask, and subsequently exposing the critical portion of the hard mask.
- In another aspect of the invention, a method of combining a wide-image mask and a loop-cutter mask includes forming a follow-on mask in a loop-cutter pattern on a portion of a hard mask, wherein the follow-on mask comprises a wide-image section and narrow-image section, and removing a portion of the hard mask left exposed by the follow-on mask. The method also includes removing at least a portion of the narrow-image section of the follow-on mask. The method also includes employing remaining wide-image sections of the follow-on mask to pattern wide-area shapes under the hard mask and follow-on mask.
- In another aspect of the invention, a combined wide-image and loop cutter mask includes a follow-on mask formed over a hard mask, and a wide-image section forming a first portion of the follow-on mask. A narrow-image section forms a second portion of the follow-on mask. The follow-on mask is configured to have the narrow-image section preferentially removed while the wide-image section remains substantially able to mask underlying films.
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FIG. 1 is an illustration of a SIT hard mask before trimming; -
FIGS. 2-5 illustrates steps in an embodiment of forming a wide-image and loop-cutter pattern in accordance with the invention; -
FIGS. 6-8 illustrates steps in an embodiment of forming a wide-image and loop-cutter pattern in accordance with the invention; -
FIGS. 9-13 illustrates steps in an embodiment of forming a wide-image and loop-cutter pattern in accordance with the invention; and -
FIGS. 14-16 illustrates steps in an embodiment of forming a wide-image and loop-cutter pattern in accordance with the invention. - The invention relates to semiconductor fabrication, and more particularly to fabricating a combination of small and large structures. In embodiments of the invention, a reduction in the number of masks required to form a final image especially when combining SIT imaging processes with traditional masking techniques is possible. In one embodiment, the method of the invention generally includes, for example, forming a follow-on mask over a section of a sidewall image transfer (SIT) loop on a substrate for further imaging the underlying substrate. The follow-on mask enables cutting the loop into segments and adds larger features to the image formed by the SIT loop, without interfering with the accuracy for those portions of the final image formed by the SIT loop.
- Referring to
FIG. 1 , ahard mask 10 image in the form of a SIT loop built using SIT-related techniques is shown. Although ahard mask loop 10 is shown, any imaging technique which builds a continuous, single-width loop, especially a single-width loop of very small and precise width, is suitable for use with embodiments of the invention. Typically, the SIT loop orhard mask 10 is on the order of a few tens of nanometers wide. However, embodiments of the invention are suitable for use with loops, or any hard mask image of virtually any size suitable for use in a semiconductor device. Also shown inFIG. 1 are dashed lines indicating thetarget shape 12 of the final image. - The
target shape 12 is the final shape to which the underlying substrate will be formed using thehard mask loop 10 and a follow-on mask. Thetarget shape 12 includes awide section 14 and anarrow section 16. Thewide section 14 of thetarget shape 12 overlaps thehard mask loop 10; whereas, thenarrow section 16 of thetarget shape 12 coincides with a portion of thehard mask loop 10. - In accordance with the invention, after forming the
hard mask loop 10, it may be necessary to cut the loop into sections plus define wide pads for contact formation. The techniques of example embodiments, as described, follow loop definition by printing of a single follow-on mask. In general, the follow-on mask should protect 1) desired portions of the SIT-defined critical-dimension masking loop; and 2) less-critical, usually wider regions to be used, for example, for long-channel devices or contact pads. Portions of loop to be removed should be left uncovered. After etch/removal of unwanted loop material, removal of the part of the follow-on mask covering critical-dimension SIT-defined lines is desirable. - Referring to
FIG. 2 , a follow-onmask 18 is formed over a portion of thehard mask loop 10. The follow-onmask 18 includes awide section 20, which corresponds to thewide section 14 of thetarget shape 12. The follow-onmask 18 also includes anarrow section 22 which corresponds to thenarrow section 16 of thetarget shape 12. The follow-onmask 18 may be formed by any of the methods well know in the art suitable for forming a follow-on mask over a hard mask loop including, expanding a desired wide-feature design by an undercut/ashback amount, and adding tabs to cover desired portions of thehard mask loop 10. - In other words, after forming a
hard mask loop 10 using SIT, the process includes printing a single follow-onmask 18. The patterns formask 18 are created by expanding desired wide-poly designs by an undercut/ashback amount, and adding tabs to cover desired SIT-defined width regions. This produces a single gate-conductor follow-on mask which is a combined wide-image and loop-cutter pattern. - Referring to
FIG. 3 , after the follow-onmask 18 has been formed, the unwanted, uncovered regions of the hardmask loop loop 10 are etched away from thesubstrate 5. The unwanted sections of thehard mask 10 may be removed using any of the suitable etching techniques well known in the art for removing the hard mask material. In other words, unwanted SIT-defined hard mask loop portions are removed/etched, without stripping resist. - Referring to
FIG. 4 , the follow-on mask 18 (seeFIG. 3 ) is etched in such a way as to reduce its length and width along its edges. Accordingly, in some instances, thenarrow section 22 of the follow-onmask 18 will be almost completely etched away. Thenarrow section 22 of the follow-onmask 18 is at least etched away sufficiently to expose the underlying critical edges of thehard mask loop 10. In other words, the process includes pulling back the follow-onmask 18 so that thenarrow section 22 covering desired portions of thehard mask loop 10 are removed (at least the critical edges of the SIT line are uncovered). - In the example of
FIG. 4 , thenarrow section 22 of the follow-onmask 18 has been completely removed to expose the underlying remaininghard mask loop 10 section. Additionally, thewide section 20 of the follow-onmask 18 has its length and width reduced to produce animage pad 24. Theimage pad 24 substantially conforms to thewide area 14 of thetarget shape 12. Additionally, the remaining exposed portion of thehard mask loop 10, formerly covered by thenarrow section 22 of the follow-onmask 18 corresponds to thenarrow section 16 of thetarget shape 12. - As noted above, the etching of the follow-on
mask 18 to form theimage pad 24 may be performed by any of the methods well known in the art suitable for etching a follow-on mask on top of ahard mask loop 10 section andsubstrate 5. - Referring to
FIG. 5 and comparing withFIG. 4 , once the combination of theimage pad 24 and the remaininghard mask loop 10 section are formed, the structure is used as a mask for etching theunderlying substrate 5. Accordingly, once theunderlying substrate 5 has been etched, a structure of theunderlying substrate 5 in the shape of thetarget shape 12 is formed where a portion of the final structure is shaped using the critical edges of the hard mask. In one embodiment, this includes etching the gate conductor stack using a combination of SIT-loop for the device-Lpoly section, plus resist pad for the wide section, and then stripping masking layers. - The final shape of the
underlying substrate 5 may additionally include astub 26 in addition to thetarget shape 12. Thestub 26 is a consequence of the pull-back process of thewide area 20 of the follow-onmask 18 exposing additional portions ofhard mask loop 10. In most applications, thisstub 26 is an inconsequential artifact which has no effect on fabrication process or the circuit design. In other applications, thestub 26 may be a beneficial component to thefinal shape 28. - Referring to
FIG. 6 , the size and overlap of the follow-mask 18 over thehard mask loop 10 is shown. Thetarget image shape 12 is shown having awide section 14 and anarrow section 16. Thenarrow section 16 of thetarget shape 12 corresponds to the critical edges of the underlyinghard mask loop 10. The follow-onmask 18 includes awide section 20 and anarrow section 22. As indicated above, one purpose of thenarrow section 22 of the follow-onmask 18 is to preserve the underlying section ofhard mask 10 during thehard mask loop 10 cutting or etching process. Thus, thenarrow section 22 of the follow-onmask 18 should extend beyond the edges of thehard mask loop 10 in order to protect those precision or critical edges. - The amount by which the follow-on
mask 18 extends beyond the edges of the underlyinghard mask loop 10 is theoverlap 32. The amount by which the follow-onmasks 18 extends beyond the edges of thewide section 14 oftarget image 12 is theextended section 30. Initially, theextended section 30 is generally larger than theoverlap 32. The amount by which thetarget image 12 is extended to form the follow-onmask 18 should preferably be sufficient so that despite follow-onmask 18 registration and image size errors, substantially all critical edges of the underlyinghard mask 10 material remain covered during the loop etching process to avoid degrading the wanted portions such as the precision edges of thehard mask 10. In other words, because preserving edges of the loop material maintains control of critical widths afforded by SIT processing, the amounts by which the original (designed) pattern of the follow-on mask is expanded (32, 30) have to be sufficient so that, despite follow-on mask registration and image size errors, all critical edges of that loop material remain covered during loop-cutting in order to prevent degrading line width control. - Referring to
FIG. 7 , an illustration of the effects of a mis-registered follow-onmask 18 is shown. In this example, the follow-onmask 44 has been formed in mis-alignment and pull-back etched. As illustrated, for this embodiment the amount of pull-back 34 need not remove the entire width ofnarrow section 22 as long as critical edges of hard-mask loop section 10 are exposed despite some amount of mis-alignment. - In many cases, the follow-on mask masking pattern over critical-Leff regions will be completely removed. Since pull-
back 34 is greater than the pattern expanded amount, a different, largerextended section 30 for pads than for device lines overlap 32 is needed. - Referring to
FIG. 8 , an example of image pad density criteria for situations where multiple image pads are densely packed is shown. The minimumimage pad space 36 density is related to the minimum lithographic pad-pad space 38 of two follow-on masks, 18 and 1 9, achievable with the method of the invention. Thus, the minimumimage pad space 36 is related to the extended section 30 (FIG. 7 ). In other words, pad shapes on follow-onmask 18 should be sufficiently far apart to allow a minimum space to print between expanded adjacent pads. - Referring to
FIGS. 9-13 , another embodiment of a combined wide-image and loop-cutter pattern is shown. Referring first toFIG. 9 , in this embodiment, ahard mask loop 10 is formed on asubstrate 5. An outline of thetarget shape 12 is shown by a dashed line. Thetarget shape 12 has awide section 14 and anarrow section 16. Also shown is the follow-onmask 46. Follow-onmask 46 has anarrow section 48 and awide section 50, corresponding to the wide andnarrow sections target shape 12. - The dimensions of the
wide section 50 of the follow-onmask 46 approximately correspond to the dimensions of thewide section 14 of thetarget shape 12. Accordingly, thenarrow section 48 of the follow-onmask 46 extends or overlaps beyond the edges of the underlyinghard mask loop 10. The edges of thewide section 50 of the follow-onmask 46 also extend beyond the edges of the underlyinghard mask loop 10 while still corresponding to the dimensions of thewide section 14 of thetarget shape 12. Additionally, an edge of thewide section 50 may be configured to coincide with edge of thehard mask loop 10. Thus, thewide section 50 of the follow-onmask 46 does not contain a section expanded beyond theunderlying image shape 12. In other words, this embodiment is similar to the previously discussed embodiment, except that while critical-width line portions of designs are expanded to make thenarrow sections 48 of follow-onmask 46, the follow-onmask pads 50 are not expanded. - Referring to
FIG. 10 , the undesired exposed portions of thehard mask loop 10 are etched from the surface of thesubstrate 5. During this process, the follow-onmask 46 protects anyhard mask loop 10 underlying the follow-onmask 46. Thus, the originalhard mask loop 10 is formed intohard mask loop 10 sections, where each section corresponds to a follow-onmask 46. - Referring to
FIG. 11 , after removal of unwanted portions ofhard mask loop 10, the follow-onmask 46 has been pulled back to form acore pad 52. Thenarrow section 48 of the follow-onmask 46 has been etched away to expose the underlyinghard loop mask 10, thus exposing the edges of thehard mask loop 10. The follow-onmask 46 may be pulled back by any of the methods well known in the art suitable for etching the material forming the follow-onmask 46, but which does not etch thehard mask loop 10 material. For example, a simple oxygen-based etch (ash) maybe used if the thickness of the follow-onmask 46 is sufficient. - Referring to
FIG. 12 , thecore pad 52 is then re-grown along its edges to expand its length and width to form animage pad 54. Theimage pad 54 is formed either over a section ofhard mask loop 10 on top of thesubstrate 5 or over acore pad 52 employed for patterning shapes not attached directly to portions of thehard mask loop 10. Thecore pad 52 is then grown back to approximately its original size using a side wall deposition and directional-etch process. The directional-etch portion of this process should have sufficient over etch to remove deposited material from the sidewalls ofhard mask loop 10, which thus must be thinner than the sidewall height ofcore pads 52. - It should be noted that re-growing the
core pad 52 to form theimage pad 54 does not reform thethin section 48 of the original follow-onmask 46 because there is no structure remaining on which to re-grow thenarrow section 48. There is no structure remaining because pull-back completely removednarrow sections 48 of the follow-onmask 46. - Referring to
FIG. 13 , after the image pad is grown, the combination (shown as reference numeral 56) of theimage pad 54 and the remaining section of thehard loop mask 10 is used as a mask to etch the final shape into theunderlying substrate 5. Once thesubstrate 5 has been etched, the image pad and section ofhard mask loop 10 are removed. It should be noted that this method of combined wide-image and loop-cutter does not produce thestub 26 shown inFIG. 5 . Additionally, the minimum pad-pad distance is decreased because thewide section 50 of the follow-onmask 46 does not need to extend beyond the edges of thetarget shape 12. - The above method allows multiple initial follow-on
masks 46 to be placed close to one another. However, image pads cannot be made with dimensions less than twice the pull-back distance, and thus either the minimum image pad size is limited or the pull-back distance is limited, both of which place size limitations on the target shape. Additionally, minimum pad-to-pad distance is decreased, but this method may be less effective for making pads with dimensions less than twice the pull-back/regrow distance plus enough to keep the desired structures in place. - Referring to
FIGS. 14-16 , another embodiment of a wide-image and loop-cutter combination pattern is shown. Beginning withFIG. 14 , asubstrate 5 has ahard mask loop 10 formed on its surface. Formed over thehard mask loop 10 is a follow-onmask 58. The follow-onmask 58 includes anarrow region 62 and awide region 60. Atarget shape 12 is indicated by the dashed lines. Thetarget shape 12 has awide area 14 and anarrow section 16. - The
narrow section 62 of the follow-onmask 58 is formed at a reduced thickness as compared to thewide section 60 of the follow-onmask 58. Thenarrow section 62 of the follow-onmask 58 is typically about 25% thinner than thewide section 60 of the follow-onmask 58 although other differences in thickness are also contemplated. Thenarrow section 62 of the follow-onmask 58 may be formed at a reduced thickness by any of the methods well known in the art for forming a thinner mask. For example, the reduced thickness ofmask 58 innarrow section 62 is formed by operating the imaging tool so thatnarrow section 62 is of a dimension approaching the resolution limits of the tool. - The follow-on
mask 58 will generally rely on degradation of resist profiles when smaller lines are printed. Additionally, it is well known to those of skill in the art that using photolithography to print “properly out of focus” narrow lines can maintain good nominal line width control, but degrade in as-developed resist height. Thus, the thinnednarrow section 62 of the follow-onmask 58 may be printed concurrently with thewide section 60 of the follow-onmask 58. Additionally, thenarrow section 62 of the follow-onmask 58 overlaps, i.e., extends beyond the critical edges of thehard mask loop 10. - After the follow-on
mask 58 is formed, the unwanted exposed portion of thehard mask loop 10 is etched or otherwise removed. Thus, the unwanted portions of thehard mask loop 10 are removed while the critical portions of thehard mask loop 10 are protected and remain intact under the follow-onmask 58. In other words, this embodiment uses a mask created from line and pad data very similar to that used for previously discussed embodiments. Also, critical SIT-defined regions have design expanded by an overlap amount so that critical edges of thehard mask loop 10 are protected despite overlay and image size variability. - Referring to
FIG. 15 , after the unwanted portions of thehard mask 10 are removed, the follow-onmask 58 is vertically etched. During the vertical etch process, the thin narrow section 62 (ofFIG. 14 ) of the follow-onhard mask 58 is preferentially removed, while the thick wide section 60 (ofFIG. 14 ) of the follow-on mask, while also being etched, will remain upon the completion of the vertical etch. Accordingly, the remaining structure includes animage pad 64 which corresponds to the originalwide section 60 of the follow-on mask and an exposed section of thehard mask loop 10. - Together, the
image pad 64 and the remaining section of thehard mask 10 form a mask corresponding to thetarget shape 12. Additionally, the critical edges of the section of thehard mask 10 are now exposed after having been protected during the hard mask etch step. In other words, vertically strip the follow-onmask 18 pattern so that the thinned areas are completely removed, but areas with full-height resist remain. - Referring to
FIG. 16 , thesubstrate 5 is etched using the combination of theimage pad 64 and remaining section of thehard mask 10 as a mask to form the final shape 66 in thesubstrate 5. The final shape 66 corresponds to thetarget shape 12 and is formed by a combination of portions of the original follow-on mask 58 (shown inFIG. 14 ) and exposed portions of thehard mask 10. - In this embodiment, the minimum pad-to-pad distance is decreased over previously discussed embodiments. Also, it is possible to design pads with small dimensions as long as they are large enough so that they do not suffer resist thinning during follow-on
mask 18 printing. - As should be now understood, in embodiments of the invention, methods include depositing on a section of the SIT loop an oversized follow-on mask of the final image, and etching the mask uniformly to leave a final large area image while removing those portions of the follow-on mask covering critical edges of the SIT loop. In general, those portions of the SIT loop having critical edges which will contribute to the final image are covered during the SIT loop cutting process. After SIT cutting, the edges are re-exposed for the final etch in order to take advantage of the high tolerances possible with SIT image forming methods.
- While the invention has been described in terms of exemplary embodiments, those skilled in the art will recognize that the invention can be practiced with modifications and in the spirit and scope of the appended claims.
Claims (20)
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US8586482B2 (en) | 2011-06-29 | 2013-11-19 | International Business Machines Corporation | Film stack including metal hardmask layer for sidewall image transfer fin field effect transistor formation |
US8580692B2 (en) | 2011-06-29 | 2013-11-12 | International Business Machines Corporation | Film stack including metal hardmask layer for sidewall image transfer fin field effect transistor formation |
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US4358748A (en) * | 1979-02-22 | 1982-11-09 | Robert Bosch Gmbh | Thin film circuit |
US5795830A (en) * | 1995-06-06 | 1998-08-18 | International Business Machines Corporation | Reducing pitch with continuously adjustable line and space dimensions |
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